The current invention relates to the synthesis of unsaturated hydrocarbyl compounds such as alkenes from enamines via hydroboration. The invention particularly relates to the stereospecific formation of the [E] isomers of such compounds.
Lewis et al., J. Chem. Soc. (B), 1969, 863 teach that enamines prepared from ketones can be subjected to hydroboration followed by hydrolysis in acetic acid to the corresponding aminoboronic acid which upon heating undergoes elimination to produce the corresponding alkenes. Borane is taught to be useful as the hydroborating agent and generally the hydroboration is conducted at reduced temperatures.
Larson et al., Tetrahedron Letters, 1975, 4005 discuss the synthesis of alkenes via the hydroboration of cyclic trimethylsilyl enol ethers. The stereospecific synthesis of unsymmetrical cyclic alkenes is taught to be possible when single isomers of the trimethylsilyl enol ethers are available as starting materials.
The existing methods for the preparation of alkenes are not without problems such as the necessity of harsh reaction conditions and the inability to obtain high yields of specific stereoisomers. Thus, what is needed is a simple process for the preparation of alkenes that operates under mild conditions and that has utility for the preparation of stereospecific isomers in high yields.